ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Steelmaking
Evaluation of Thermodynamic Driving Force and Effective Viscosity of Secondary Steelmaking Slags on the Dissolution of Al2O3-Based Inclusions from Liquid Steel
Pedro Cunha AlvesVinicius Cardoso Da RochaJulio Aníbal Morales PereiraWagner Viana Bielefeldt Antônio Cezar Faria Vilela
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2021 Volume 61 Issue 7 Pages 2092-2099

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Abstract

Dissolution of Al2O3-based inclusions are paramount during production of special steel and slag engineering is key to enhance this phenomenon. This work evaluates the influence of thermodynamic driving force (ΔC) and effective viscosity (ηe) on steel cleanliness of three distinct steel grades and slag composition (Steel/Slag A, Steel/Slag B and Steel/Slag C). Initial and final steel and slag samples were withdrawal on an electric steelmaking facility. The first samples after addition of aluminum as deoxidizer and the second after vacuum degassing stage. X-ray fluorescence and optical spectrometry obtained initial and final samples chemical composition. An ASPEX Explorer acquired inclusions data and FactSage v.7.2 performed thermodynamic calculations. Analysis of steel Al and O content highlighted an inefficient dissolution of Al2O3-based inclusions for Steel/Slag A, deteriorating steel cleanliness. Furthermore, this phenomenon is supported by average inclusions composition on initial and final samples plotted in pseudo-ternary diagram. Steel/Slag B and C provided improved results regarding the dissolution of Al2O3-based inclusions with a final inclusion density below 0.50 mm-2. These two slags composition achieved values of ΔC above 25 and ηe close to 0.10 Pa·s. In addition, their combined effect (ΔC/ηe) presented values above 250 and had the highest linear fit among these analyses. These properties are influenced by slags chemical composition and can be improved controlling parameters as binary basicity and CaO/Al2O3 ratio. Slags B and C were selected to define an optimal range for these parameters, with binary basicity between 3.00–3.50 and CaO/Al2O3 ratio in a range from 2.50–3.50.

Inclusions average chemical composition on initial and final steel samples as contour lines plotted in CaO–Al2O3–SiO2 and CaO–MgO–Al2O3 ternary diagram (a) Steel A; (b) Steel B; (c) Steel C. Fullsize Image
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© 2021 The Iron and Steel Institute of Japan.

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs license.
https://creativecommons.org/licenses/by-nc-nd/4.0/
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